AIR Worldwide’s latest report on Typhoon Usagi describes a “Category 3 storm with maximum sustained winds of 204 km/h [127.5 mph].” It is “expected to strengthen over the coming days and could become the first Category 5 storm of 2013.”
Usagi is currently located several hundred miles off the coasts of both the northern Philippine island of Luzon and Taiwan and is gathering strength as it moves northwest. The typhoon, called Odette in the Philippines, is “expected to deliver heavy rains to the Philippines, including the capital Manila, and strong winds and heavy rains to Taiwan. The eye of the storm is expected to pass near Taiwan’s southern tip at about 06:00 GMT, or 2 p.m., local time, on September 21, and then make landfall as a Category 3 typhoon in China late Sunday, local time near Hong Kong.”
According to AIR, “the northern area of Luzon is not heavily insured due to low commercial and industrial activity. Cyclone coverage typically excludes loss or damage from flood, tidal wave, high water, or overflow, regardless of whether it is caused by high winds. Significant insurance losses in the Philippines are not expected from this event.”
AIR also indicated that it doesn’t “expect significant wind loss in Taiwan, but there could be significant flood loss. Due to orographic lifting combined with occasional South China Sea monsoon-scale influences, it is not uncommon for more than 1,000 mm of precipitation to fall during the passage of a tropical cyclone. In addition, insured wind and flood losses in Hong Kong are not expected to be significant.”
Philippine officials issued warnings for flash flooding, landslides and storm surges for seven northern provinces on Thursday, which will remain in force until Sunday. Taiwan is expected to issue a sea alert Thursday and a land alert Friday. On September 19th at 7 p.m. local time, China’s National Meteorological Center issued a yellow alert for the typhoon, the third highest on the country’s four-tier weather warning system.
“Usagi is currently over the Philippine Sea about 900 kilometers (560 miles) southeast of Taiwan’s southernmost Hengchun peninsula,” said Dr. Peter Sousounis, senior principal scientist, of AIR Worldwide. “The storm is expected to intensify a bit more as it passes over warm waters and low wind shear conditions and before it feels the frictional effects of Taiwan’s mountainous terrain.
“Usagi will pass very close to the southern tip of Taiwan at 2 p.m. local time (6:00 UTC) Saturday, and interaction with land could potentially weaken the storm. Usagi is expected to weaken to a Category 2 typhoon by the time it makes landfall near Hong Kong late Sunday or early Monday, with winds just under 178 km/h [111 mph]. The Joint Typhoon Warning Center (JTWC), which is currently measuring Usagi as a Category 5 super typhoon with maximum sustained winds of at least 252 km/h [157.5 mph], expects Usagi to weaken to a Category 3 storm by the time it reaches Hong Kong.”
Dr. Sousounis also said: “Rain will soak Manila and parts of northern Philippines as Typhoon Usagi moves westward through the Luzon Strait. Manila is prone to flooding during the heavy rains of the summer monsoon season. Western and northern Luzon will be most prone to flooding between Friday and Monday. The brunt of the powerful storm’s severe winds should, in the Philippines, impact only some small northern islands and perhaps the northern tip of mainland Luzon.”
He indicated that the eye of the storm is “expected to pass just south of Taiwan. Tropical cyclones typically weaken rapidly upon interaction with the central mountain range and because the eastern coast of Taiwan is relatively unpopulated, heavy wind losses tend to be restricted to the west coast of Taiwan. The highest flood risk is along the southwestern mountains.”
According to AIR, “Hong Kong is sheltered by the coastal mountains; therefore, the wind risk in the region is relatively low. The flood risk is also quite low because of the very sophisticated flood defense system that has been implemented in and around Hong Kong.”
In the Philippines, however, AIR noted that “lighter materials, such as wood frame with galvanized iron or aluminum roofs, are often used for residential buildings in rural areas. In contrast, urban residential structures are generally made of concrete block with metal roofs, although hollow concrete is also used.
“Masonry residences can also be found in the cities, which also have many high-rise apartments made of steel construction. Masonry is often used for smaller commercial establishments, although the majority of all commercial and industrial buildings are reinforced concrete or steel. Building codes are not strictly enforced. In the Luzon area, one- to- two story buildings of mixed construction (concrete and wood) are common.
“The majority of low- to mid-rise residential buildings in Taiwan are constructed with reinforced concrete frames and brick infill walls, although some older residential masonry buildings exist as well. Taller buildings are typically constructed using reinforced concrete frames and shear walls.
“The commercial and industrial stock in Taiwan is relatively evenly split between steel and reinforced concrete construction. At the level of expected wind speeds at landfall, unreinforced masonry construction in Taiwan may experience minor to moderate levels of damage. However, the majority of damage is likely to be limited to nonstructural elements such as roof covering, glazing, and cladding. Well-engineered high-rise buildings should experience only minor damage to windows broken from flying debris and damage to cladding and roofing from wind-driven rain.
“Also, houses in coastal regions of Guangdong are commonly masonry or reinforced concrete with clay tile roofs, which perform reasonably well in the face of typhoon winds. In Hong Kong, the typhoon’s strong winds could damage roof and wall claddings of poorly constructed homes and commercial structures. There is likely to be little damage to well-built structures within Hong Kong.”
Dr. Sousounis concluded, “As is often the case with China typhoons, flooding is a major concern; with much of the population located near waterways and along the coast, many homes and businesses are at risk.”
Source: AIR Worldwide